An attempt has hitherto been made to form a thin film of an inorganic material or an organic material on a base material film and thus to develop a high level of gas barrier properties by the gas barrier film. For example, Japanese Patent Application Laid-Open No. 313560/2005 proposes a gas barrier film having a laminated structure comprising a flexible base material, and a 0.1 to 10 μm-thick acrylic resin layer of a cured product of a UV curable resin containing only an acrylic monomer and/or an acrylic polymerizable prepolymer as a polymerizable component and a 20 to 100 nm-thick inorganic barrier layer stacked in that order from the flexible base material side on one side or both sides of the flexible base material.
The claimed advantage of the techniques disclosed in the above patent documents is that the formation of a UV cured resin layer having a specific thickness using a specific UV curable resin directly on a flexible base material followed by stacking of an inorganic barrier layer having a specific thickness on the UV cured layer can provide a gas barrier film that, while enjoying good gas barrier properties, hardly causes curling in the production process of the gas barrier film. For example, SiOx, AlOx, SiOxNy, SiNx, SiOxNyCz, SiNxCy, AlOxNy, AlNx, AlOxNyCz, and AlNxCy are exemplified as ceramic materials for use in the inorganic barrier layer.
In this film, a combination of an acrylic resin film having a specific thickness with a gas barrier film having a specific thickness formed of an inorganic material has simultaneously realized gas barrier properties of the gas barrier sheet and the suppression of curling.
From the viewpoint of improving the productivity of the gas barrier sheet, however, there is a demand for simultaneous realization of the gas barrier properties and the suppression of curling by the gas barrier film alone.
Organic EL displays are thin and have a variable shape, that is, are flexible and thus are expected as next-generation flat-panel displays. The organic EL displays, however disadvantageously suffer from low water resistance. Specifically, when water or oxygen invades through defects such as pin holes present on a cathode surface in an organic EL display, nonluminescent areas are formed due to oxidation of a cathode metal and interfacial peeling between the cathode metal and the organic compound. These nonluminescent areas significantly deteriorate display quality and, at the same time, leads to lowered brightness. Such nonluminescent areas are generally called “dark spots” or “black spots.” In order to suppress the occurrence of the dark spots or black spots and to ensure the display quality, the invasion of water or oxygen into the organic EL display should be suppressed. To this end, an attempt has been made to apply a gas barrier sheet to the organic EL display.
In the application of the gas barrier sheet to the organic EL display, a high level of gas barrier properties are required of the gas barrier sheet from the viewpoint of guaranteeing a good display quality of the organic EL display. Specifically, the gas barrier sheet should have a gas permeability of one-hundredth or one-thousandth or less of the gas permeability required in food-related fields where gas barrier sheets are generally used. Accordingly, in order to apply the gas barrier sheet to the organic EL display well, a gas barrier sheet having a higher level of gas barrier properties than the conventional gas barrier sheet should be developed.
A heat cycle test may be mentioned as one of durability evaluation tests of the organic EL display. In the heat cycle test, the procedure of holding the organic EL display at an elevated temperature for a given period of time is repeated to evaluate the durability of the organic EL display. Therefore, also when the gas barrier sheet is applied to the organic EL display, it is desirable that the gas barrier sheet provided in contact with the organic EL display does not cause deformation such as curling and a deterioration in gas barrier properties upon exposure to the heat cycle test.